Intrusion detector

ABSTRACT

An intrusion detector comprising a passive sensor for detecting a person entering a space to be monitored, said intrusion detector comprising a housing provided with a window for said passive sensor, optical means for directing electromagnetic radiation from said person onto the passive sensor, alarm means connected to said passive sensor for generating an alarm in case the electromagnetic radiation from said person being detected by the passive sensor corresponds to a signal value that exceeds a maximum level or falls below a minimum level, a special feature being the fact that the optical means are provided with a mirror curved in two directions for forming at least one protective curtain extending in a vertical plane in the space to be monitored, wherein the passive sensor is disposed on the optical axis at the focus of the mirror, and wherein the mirror directs a beam of electromagnetic radiation from the person, rotated through at least 45°, preferably through at least substantially 90°, onto the passive sensor.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention relates to an intrusion detector comprising a passivesensor for detecting a person entering a space to be monitored, saidintrusion detector comprising a housing provided with a window for saidpassive sensor, optical means for directing electromagnetic radiationfrom said person onto the passive sensor, alarm means connected to saidpassive sensor for generating an alarm in case the electromagneticradiation from said person being detected by the passive sensorcorresponds to a signal value that exceeds a maximum level or fallsbelow a minimum level.

2. Background

Such an intrusion detector is known from the present Applicant'sInternational (PCT) patent publication No. 2006/107203. Disposed behindthe window of the housing of the known intrusion detector is a passiveinfrared sensor in the form of a pyro-electrical sensor which issensitive to infrared light in the far infrared wavelength range. When aburglar, for example, enters the space to be monitored, infrared light(with a wavelength of 6-50 μm) emitted by the burglar (on account of theburglar's body heat) will be detected by the pyro-electrical sensorfunctioning as a passive infrared sensor, and subsequently an alarmsignal will be generated. The intrusion detector, through itspyro-electrical sensor, thus functions as a motion detector. To preventthe intrusion detector being sabotaged while in its state of rest, forexample when the pyro-electrical sensor is deactivated during thedaytime, for example as a result of lacquer or paint being sprayed onthe window or of the intrusion detector as a whole being covered with ahat, a coat or the like, the known intrusion detector is configured witha so-called “anti-masking” or “anti-sabotage” system. Said system thusfunctions to protect the intrusion detector generally against sabotageattempts, in particular against being approached, masked or damaged.Such “anti-masking” systems generally comprise a light source and alight detector optically coupled thereto, which “monitor” the directvicinity of the housing as well as the window. When a person approachesthe housing and/or the window therein, this will lead to a significantincrease or decrease (viz. diffusion/reflection or absorption of emittedlight by the person) of the light being detected by the light detectorand consequently to an alarm signal being generated.

U.S. Pat. No. 4,375,034 (Guscott) likewise discloses a passive infraredintrusion detection system disposed in a space to be monitored. Theintrusion detection system disclosed therein comprises a focussingmirror and a cylindrical mirror which cooperates therewith to form aprotective curtain in the space to be monitored, with a pyro-electricalsensor being disposed on the optical axis at the focus of the focussingmirror. When an intruder moves through the protective curtain—in theoperative condition of the intrusion detection system—the focussingmirror will focus infrared light emitted by the burglar (on account ofthe latter's body heat) onto the pyro-electrical sensor via thecylindrical mirror, which will detect said infrared light. Detectionsignals corresponding thereto are subsequently electronically processedin order to produce an alarm output to signal the presence of theintruder.

A drawback of the use of several protective curtains as described in theaforesaid U.S. Pat. No. 4,375,034 in passive infrared intrusiondetectors known from the aforesaid International (PCT) patentpublication No. 2006/107203 is that only a limited number of protectivecurtains can be formed, whilst in practice there is a growing need for ahigher monitoring density, i.e. a larger number of protective curtains.After all, the passive sensor, for example a pyro-electrical sensorwhich is sensitive to infrared light, has a limited aperture angle,which limits the number of focusing mirrors to be used. Moreover, theuse of a larger number of smaller focussing mirrors does not offer asolution, since this would have a disproportionate adverse effect on thedesired signal/noise ratio.

SUMMARY OF THE INVENTION

The object of the invention is to provide an improved intrusion detectorcomprising a passive sensor for detecting a person entering a space tobe monitored, wherein in particular a higher monitoring density, i.e. alarger number of protective curtains, can be realised.

In order to accomplish that object, an intrusion detector of the kindreferred to in the introduction is characterised in that the opticalmeans are provided with a mirror curved in two directions for forming atleast one protective curtain extending in a vertical plane in the spaceto be monitored, wherein the passive sensor is disposed on the opticalaxis at the focus of the mirror, and wherein the mirror directs a beamof electromagnetic radiation from the person, rotated through at least45°, preferably through at least substantially 90°, onto the passivesensor. An at least substantially vertical beam of infrared radiation,for example from an intruder, is thus directed onto the passive sensorin the focus of the mirror, preferably rotated through 90°. In otherwords, an entering beam of infrared radiation from a vertical object(i.e. a person) emitting infrared radiation is reflected to the focus bythe double-curved mirror. This takes place in such a manner that thevertical radiation beam takes effect in the focus through summation ofconverging reflection images. The use of such a mirror curved in twodirections makes it possible to form at least one additional protectivecurtain in combination with the prior art protective curtains alreadyrealised, without there being any question of mutual interference andwithout the desired signal-noise ratio being adversely affected.

In a preferred embodiment of an intrusion detector according to theinvention, the mirror has a mirror-symmetrical configuration for formingat least two protective curtains extending in a vertical plane in thespace to be monitored. Said protective curtains are in particularpositioned mirror symmetrically relative to a plane of mirror symmetryof the mirror. In this way two (additional) protective curtains arerealised on either side of the aforesaid plane of mirror symmetry.

In another preferred embodiment of an intrusion detector according tothe invention, the mirror is paraboloid in shape. In particular, theparaboloid mirror has a smooth, for example polished, work surface. Inanother preferred variant, the paraboloid mirror has a segmented worksurface.

In another preferred embodiment of an intrusion detector according tothe invention, the paraboloid mirror comprises at least two groups ofmirror segments, each group of mirror segments being arranged forforming a protective curtain. Preferably, four mirror segments areprovided for each group of mirror segments, so that two (additional)protective curtains are realised. A mirror segment of one grouppreferably has an angle of inclination or declination (α) and an azimuthangle (β), whilst a mirror segment of another group, which is mirroredtherewith, has an angle of inclination or declination α) and an azimuthangle (−β). Mirrored mirror segments thus have the same angle ofinclination or declination (both as regards size as regards sign),whilst the azimuth angle of mirrored mirror segments is the same asregards size but different as regards sign (viz. + and −).

In another preferred embodiment of an intrusion detector according tothe invention, the mirror is made in one piece, for example of plasticmaterial or a metal.

The invention may be combined with a motion detection system accordingto the present Applicant's European patent No. 0 967 847. In the presentcase this means that means are provided for measuring the shape of andthe phase relation between first and second detection signals (X, Y)which are measured when an intruder moves through spatially separatedprotective curtains. This makes it possible to double the number ofprotective curtains again without any mutual interference, which leadsto an even higher monitoring density.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in more detail with reference tofigures illustrated in a drawing, in which

FIG. 1 is a perspective, schematic view of an intrusion detector asdescribed in the aforesaid International (PCT) patent publication No.2006/107203;

FIG. 2 is a perspective and schematic view of a paraboloid mirror (12)according to the invention, which may be used in the intrusion detectorof FIG. 1; and

FIGS. 3 and 4 are schematic views of protective curtains associated withthe paraboloid mirror (12) of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a perspective, a schematic view of a prior art passiveinfrared intrusion detector disposed in a space to be monitored,comprising a housing 1 of plastic material, which is made up of a lowerhousing 2 and an upper housing 3 mounted thereon, a window 4, as well asan alarm light 5. The alarm light 5 lights up in case an alarm isgenerated when an undesirable object enters the room to be monitored. Ifdesired, said entry is reported to an alarm centre. Disposed behind thewindow 4 is a passive infrared sensor configured as a pyro-electricalsensor (not shown in FIG. 1), which is sensitive to infrared light inthe far infrared wavelength range. When a burglar, for example, entersthe room to be monitored, infrared light emitted by the burglar (onaccount of the burglar's body heat) will be detected by thepyro-electrical sensor, whereupon an alarm signal will be generated. Theintrusion detector thus functions as a motion detector. To prevent theintrusion detector being sabotaged while in a state of rest, for examplewhen the pyro-electrical sensor is deactivated during the daytime, theintrusion detector is configured with an improved “antimasking” systemor “anti-sabotage” system. As already noted before, said systemfunctions to protect the intrusion detector generally against sabotageattempts, in particular against being approached, masked or damaged. Theradiation path shown in FIG. 1 relates to a so-called “anti-masking”system or “anti-sabotage” system of this known passive infraredintrusion detector, in which use is made of infrared light sources 6, 7,8 for photodiodes 9, 10 sensitive to near-infrared light, and also of anL-shaped light guide 11, for example of polycarbonate. For more detailedinformation regarding the operations of said system, reference is madeto the aforesaid International (PCT) patent publication No. 2006/107203.

FIG. 2 is a perspective and schematic view of a paraboloid mirror 12according to the invention, which may be used in the intrusion detectorof FIG. 1. The mirror 12 is in this case mirror-symmetrical relative toa plane 13 of mirror-symmetry. The mirror 12 further comprises asegmented work surface 14. Said work surface 14 consists of two groupsof mirror segments, each consisting of four mirror segments A,B,C,D andA′,B′,C′ and D′. As FIG. 3 shows, one (the “left-hand”) group comprisingmirror segments A,B,C,D disposed horizontally in the mirror 12 providesa vertical protective curtain 15. Said protective coating 15 ispositioned to the right of the plane 13 of mirror-symmetry, seen fromthe mirror 12. Similarly, the other (the “righthand”) comprising mirrorsegments A′,B′,C′,D′ disposed horizontally in the mirror 12 provides avertical protective curtain 16, which is positioned to the left of theplane 13 of mirror-symmetry, seen from the mirror 12 (see FIG. 4). It isnoted that a mirror segment A,B,C,D of one group has an inclinationangle (α) and an azimuth angle (β), in which a mirror segmentA′,B′,C′,D′ of the other group, which is mirrored therewith, has aninclination angle (α) and an azimuth angle (−β). The mirror segmentsA,B,C,D on the one hand and A′,B′,C′,D′ on the other hand havedeclination of, for example, 3.6°, 6.3°, 8.9° and 11.8°, respectively,whilst the azimuth angle of the mirror segments C,C° is −8.1° and −8.1°,respectively. As FIG. 3 shows, the pyro-electrical sensor comprises twois sensitive elements of opposite polarity. Each element has a width of1 mm and a length of 2 mm, for example, whilst the zones are for example1 mm apart (viz. one 0.5 mm to the left of the focus and the other 0.5mm to the right of the focus, for example). If the focal distance is forexample 30 mm from the mirror surface, the detection beam can berecognized from about 30 cm.

FIG. 4 is another schematic view of the protective curtains 15, 16 asformed by the segmented work surface 14 of the paraboloid mirror 12. Inthis case, however, nine further protective curtains are shown as well,which protective curtains are formed by a mirror 17 as shown in FIG. 2.Thus, a total of 11 protective curtains are provided, which do notinterfere with each other and which realise a higher monitoring density,without the desired signal-noise ratio being adversely affected. Themirrors 12, 17 of FIG. 2 are made in one piece, for example of plasticmaterial.

From FIGS. 3 and 4 it will be understood that the mirror 12 will directa vertical infrared radiation beam from a burglar, for example, which iscoupled into the mirror 12, onto the pyro-electrical sensor as ahorizontal infrared radiation beam.

It is noted that the invention is not limited to the embodiment asdescribed herein, but that it also extends to other preferred variants.Thus, a person skilled in the art will appreciate that the paraboloidmirror 12 does not necessarily have to be mirror-symmetrical, in thesense that (i) one group of mirror segments A,B,C,D may suffice forforming one protective curtain, or that (ii) two identical groups ofmirror segments A,B,C,D and A′,B′,C′,D′, respectively, (each having thesame angle of inclination of declination and the same azimuth angle) maybe used for realising two adjacent protective curtains.

1. An intrusion detector, comprising: a passive sensor configured todetect electromagnet radiation associated with an object entering anarea to be monitored; optical means configured to direct theelectromagnetic radiation associated with the object to the passivesensor, wherein the optical means are provided with a mirror curved intwo directions on a vertical axis for forming at least one protectivecurtain extending in a vertical plane in the area to be monitored,wherein the mirror comprises at least two groups of mirror segments, andwherein a first mirror segment of one group has a first mirror segmentinclination/declination angle equal to α and a first mirror segmentazimuth angle equal to β, and a second mirror segment of a second grouphas a second mirror segment inclination/declination angle equal to α anda second mirror segment azimuth angle equal to −β; and an alarm unitconnected to the passive sensor, the alarm unit configured to generatean alarm in the event that a value corresponding to the electromagneticradiation associated with the object being detected by the passivesensor is greater than a maximum value or less than a minimum value,wherein the passive sensor is disposed on an optical axis at a focaldistance of the first mirror segment and the second mirror segment. 2.The intrusion detector according to claim 1, wherein the mirror has amirror-symmetrical configuration forming at least two protectivecurtains extending in the vertical plane in the area to be monitored. 3.The intrusion detector according to claim 2, wherein the at least twoprotective curtains are positioned mirror-symmetrically relative to aplane of mirror-symmetry of the mirror.
 4. The intrusion detectoraccording to claim 1, wherein the mirror is paraboloid in shape.
 5. Theintrusion detector according to claim 4, wherein the paraboloid mirrorhas a smooth work surface.
 6. The intrusion detector according to claim5, wherein the paraboloid mirror has a segmented work surface.
 7. Theintrusion detector according to claim 1, wherein each group of mirrorsegments comprises four mirror segments.
 8. The intrusion detectoraccording to claim 1, wherein each group of mirror segments comprisesgreater than four mirror segments.
 9. The intrusion detector accordingto claim 1, wherein the mirror is made in one piece.
 10. An intrusiondetector, comprising: a passive sensor configured to detectelectromagnet radiation associated with an object entering an area to bemonitored; optical means configured to direct the electromagneticradiation associated with the object to the passive sensor, wherein theoptical means are provided with a mirror curved in two directions on avertical axis for forming at least one protective curtain extending in avertical plane in the area to be monitored, wherein the mirror comprisesat least two groups of mirror segments, each group of mirror segmentsbeing arranged for forming a protective curtain, and wherein a firstmirror segment of one group has a first mirror segmentinclination/declination angle equal to α and a first mirror segmentazimuth angle equal to β, and a second mirror segment of a second grouphas a second mirror segment inclination/declination angle equal to α anda second mirror segment azimuth angle equal to −β; and an alarm unitconnected to the passive sensor, the alarm unit configured to generatean alarm in the event that a value corresponding to the electromagneticradiation associated with the object being detected by the passivesensor is greater than a maximum value or less than a minimum value,wherein the passive sensor is disposed on an optical axis at a focaldistance of the mirror, and wherein the mirror directs beams ofelectromagnetic radiation from the object to the passive sensor suchthat a summation vertical radiation beam takes effect in the focaldistance of the mirror.